1. Field of Invention
The invention relates to an optical information storage medium and method for manufacturing the same and, in particular, to the optical information storage medium, which is a single side dual layer DVD-R, and method for manufacturing the same.
2. Related Art
Along with the coming multi-media generation, the electronic products need higher storage density and higher capacity in storage medium. Traditionally, the storage medium is divided into two categories. One is magnetic recording medium and the other is optical recording medium. The optical recording medium, which includes read only memory CD (CD-ROM), write-once CD (CD-R), rewritable CD (CD-RW), read only memory DVD (DVD-ROM), write-once DVD (DVD-R), rewritable DVD (DVD−RW, DVD+RW), and random memory DVD (DVD-RAM), gets the lager market share.
Facing the problem of fast growing information capacity needs, it is the goal of the industry to increase the storage capacity of storage medium. DVD has a larger information storage capacity, and, as a result, it has gained a giant share of the market. There are several kinds of DVD, such as single side single layer, dual side single layer, single side dual layer, and dual side dual layer. The storage capacities of these discs range from 4.7 GB to 17 GB.
If there is only one side with information data while the other side is a dummy, the capacity of the disc is about 4.7 GB, which is called a single side single layer DVD or DVD-5. If there is one side with dual layer information data, the capacity of the disc is about 8.5 GB, which is called a single side dual layer DVD or DVD-9. If utilizing the dual side dual layer technique, the capacity could be increased to 13.2 GB, which is called DVD-14, or 17 GB, which is called DVD-18. At present time, consumers have more acceptability on single side single layer DVD-5 and DVD-9 than others, because they do not have to “turn over the disc”.
Owing to large capacity and write-once feature, the single side single layer DVD-R also attracts people's attention. As shown in FIG. 1, conventional single side single layer DVD-R 10, has a first substrate 11, a first recording stack L0 12, a spacer layer 13, a second recording stack L1 14, and a second substrate 15. In this case, the first recording stack L0 12 and the second recording stack L1 14 are coated on the data side of the first substrate 11 and the second substrate 15 separately. The spacer layer 13 is sandwiched between the first recording stack L0 12 and the second recording stack L1 14. When reading data, the laser passes through the first substrate 11 to focus on the first recording stack L0 12 or passes through the spacer layer 13 to focus on the second recording stack L1 14.
The first recording stack L0 12 has a complex refractive index, RL0, and a transmission value TL0. The second recording stack L1 14 has a complex refractive index, RL1. To fit the requirement of standard DVD-ROM player, the following conditions are fulfilled in the single side single layer DVD-R: 0.45≦TL0≦0.75, 0.18≦RL0≦0.30, and 0.40≦RL1≦0.80. But in the real manufacturing process, the reflectivity of the phase change material is usually low (about 7%), it can not meet the requirement of the standard DVD-ROM player. Such low reflection values severely reduce read-back compatibility on existing DVD players.
Generally, the first recording stack L0 includes a recording layer and a reflective layer and the second recording stack L1 also includes a recording layer and a reflective layer.
According to a larger storage capacity single side single layer DVD-R 20 in the prior art, the manufacture processes are divided into two different kinds. One is photo-polymerization process (2P process), and the other is non-2P process. Hereafter, the two processes are introduced.
1. 2P process: referring to FIG. 2, a first organic dye layer 22 and a first reflective layer 23 are formed on a pre-grooved first substrate 21 by spin coating. Spraying a photo-setting resin 25 on a pre-grooved master 24, then pressing the first reflective layer 23 and the master 24. After the radiation to solidify the resin, a spacer layer 26 is formed. Peeling off the master 24, a second organic dye layer 27 and a second reflective layer 28 are formed on the grooved spacer layer 26. Finally, a second substrate 29 is formed.
2. Non 2P process: referring to FIG. 3, a first recording layer 22′ and a first reflective layer 23 are formed on a pre-grooved first substrate by sputtering or evaporation. A second reflective layer 28 and a second recording layer 27′ are sputtered or evaporated sequentially on a pre-grooved second substrate 29. In the case, the first recording layer 22′ and the second recording layer 27′ are made of phase change material. The first reflective layer 23 and the second recording layer 28 are bonded by photo-setting resin 25. A spacer layer 26 is formed after solidifying the photo-setting resin 25 and the process is completed.
However, owing to the peeling off step of 2P process, the yield of the process is usually low, which increase the cost of manufacturing process.
On the other hand, the discs made by non 2P process although avoid the peeling off step, and the yield of the process is improved. But the phase change material still can not meet the requirement of the dual layer reflectivity of DVD-ROM standard, also limit the market size.
Referring to FIG. 4, if replace the phase change material with the organic dye as the recording layer, and spin-coat it to form the reflective layer and recording layer, the surface of the grooves on the first substrate 21 and the second substrate 29 will be flatten. Because of the flatness of the groove pattern G between the spacer layer 26 and the second organic dye layer 27, it is difficult for the pickup head of DVD player to tacking and leads to a bad signal while writing on the disc.
As described above, it is an important subjective to provide an optical information storage medium and method for manufacturing the same to solve the above-mentioned problems.